This invention relates to a brushless motor.
Some brushless motors include each a rotor having a plurality of segment magnets. For example, JP-A-2001-359266 discloses a brushless motor including a rotor with a plurality of segment magnets attached on an outer periphery of an annular rotor core.
In JP-A-2001-359266, the segment magnets are stacked at a plurality of stages in the axial direction of the rotor core. The segment magnets configuring each stage are arranged with an equal spacing in the circumferential direction of the rotor core. The segment magnets configuring each stage are arranged so as to be shifted in phase with those at any other stage in the circumferential direction of the rotor core. That is, the rotor has a configuration of a so-called stage skew arrangement.
However, in the rotor described in JP-A-2001-359266, if the number of the stacking stages of the segment magnets and the number of the pole angular aperture of each segment magnetic, etc., are not properly set, it becomes impossible to properly polarize the unpolarized segment magnets attached on the rotor core. That is, if the number of the stacking stages of the segment magnets and the number of the pole angular aperture of each segment magnetic, etc., are not proper, two magnetic poles of N and S poles occur in the outer surface of the same segment magnet polarized after the segment magnet is attached on the rotor core.
Even though already polarized segment magnets are attached on the rotor core, it is difficult to attach the segment magnets on the rotor core with good position accuracy because the segment magnets have already magnetized; this is a problem.